A wheel bearing apparatus with a rotational speed detecting apparatus is generally known that can support a wheel of a vehicle with respect to a suspension apparatus. Also, the wheel bearing apparatus detects a rotation speed of a wheel of vehicle to control the anti-lock braking system (ABS). Such a bearing apparatus generally includes a sealing apparatus arranged between the inner and outer members that rotates relative to each other, via rolling elements contained between them. The rotational speed detecting apparatus includes a magnetic encoder with magnetic poles alternately arranged along its circumference integrally formed with the sealing apparatus. A rotational speed sensor detects change of magnetic poles of the magnetic encoder caused by the rotation of a wheel.
In general, the rotational speed sensor is mounted on a knuckle after the wheel bearing apparatus has been mounted on the knuckle, forming part of a suspension apparatus. Recently, a wheel bearing apparatus with a rotational speed detecting apparatus has been proposed. Here, a rotational speed sensor is also contained within a wheel bearing in order to reduce the whole size of the wheel bearing apparatus and to eliminate the complexity of the adjustment of an air gap between the rotational speed sensor and a magnetic encoder.
A structure shown in FIG. 13 is one example of the wheel bearing apparatus with a rotational speed detecting apparatus. This wheel bearing apparatus has an outer member 51, secured on a knuckle (not shown), that forms a stator member. An inner member 52 is inserted into the outer member 51, via double row balls 53, 53. The inner member 52 has a wheel hub 55 and an inner ring 56 fit onto the wheel hub 55.
The outer member 51 has an integrally formed body mounting flange 51b. The outer member 51 inner circumference is formed with double row outer raceway surfaces 51a, 51a. The inner member 52 is formed with double row inner raceway surfaces 55a, 56a on its outer circumference. The double row inner raceway surfaces 55a, 56a are arranged opposite to the outer member double row outer raceway surfaces 51a, 51a. One inner raceway surface 55a, of the double row inner raceway surfaces 55a, 56a, is formed on the outer circumference of the wheel hub 55. The other double row inner raceway surfaces 55a, 56a is formed on the outer circumference of the inner ring 56. The inner ring 56 is press-fit onto a cylindrical portion 55b that axially extends from the inner raceway surface 55a of the wheel hub 55. The double row balls 53, 53 are contained between the outer and inner raceway surfaces and rollably held by cages 57, 57.
The wheel hub 55 has, on its one end, a wheel mounting flange 54 to mount a wheel (not shown). The inner ring 56 is axially immovably secured by a caulked portion 58. The caulked portion 58 is formed by plastically deforming radially outward the end of the cylindrical portion 55b. The outer-side end of the outer member 51 has a seal 59. The inner-side end of the outer member 51 has a cover 63 to prevent leakage of lubricating grease contained in the wheel bearing and the entry of rain water or dust into the wheel bearing from outside.
An encoder 60 is press-fit onto the outer circumference of the inner ring 56. The encoder 60 has an annular supporting member 61 formed from magnetic metal sheet. The supporting member 61 has a substantially L-shaped cross-section. An encoder body 62 is adhered to the side surface of the annular supporting member 61. The encoder body 62 is formed as a permanent magnet from rubber blended with ferrite powder. The encoder body 62 has N and S poles alternately arranged along its circumference.
The cover 63 is formed of synthetic resin with a lidded cylindrical configuration. Its cylindrical portion 63a is press-fit into the inner circumference of the inner-side end of the outer member 51. Its lid portion 63b closes an open end of the outer member 51. The cylindrical portion 63a is integrally formed with a flange 64 that enables exact positioning of the whole cover 63 relative to the outer member 51. Thus, this easily controls the position of a sensor 69 mounted on the cover 63.
As shown in FIG. 14, the lid portion 63b of the cover 63 is integrally formed with a cylindrical sensor mounting portion 65. An insertion portion 69a of the sensor 69 is inserted into a sensor mounting bore 66 formed in the sensor mounting portion 65. In addition, a metal core 67, of the lidded cylindrical configuration, is integrally molded with the cover 63 over a region from the inner circumference of the cylindrical portion 63a to the inside surface of the lid portion 63b. The metal core 67 has a cylindrical portion 67a integrally molded with the cover cylindrical portion 63a. Also, it includes a lid portion 67b that forms a bottom portion of the cylindrical portion 67a. An opening portion of the sensor mounting bore 66, opposing the encoder body 62, is closed by the metal core lid portion 67b. 
The metal core 67 is formed of non-magnetic steel sheet material with a thickness of about 0.3 mm. The lid portion 67b increases the strength of the cover 63. The non-magnetic material does not give any adverse influence to the detecting accuracy of the rotational speed.
The sensor 69 has a synthetic resin body and is mounted on the cover 63 by inserting the inserting portion 69a into the cover sensor mounting bore 66. The inserting portion 69a contains a detecting portion and a tip end. The detecting portion (not shown) detects a variation of magnetic flux generated by rotation of the magnetic encoder 60 at a position near the tip end of the inserting portion 69a. The tip end of the inserting portion 69a is arranged opposite to the encoder body 62, via a predetermined axial gap, sandwiching the metal core lid portion 67b therebetween. Signals from the detecting portion are output via a cable 68.
Since the opening portion of the cover sensor mounting bore 66, opposing the encoder body 62, is closed by the metal core lid portion 67b, a path for foreign matter entering into the inside of the wheel bearing apparatus is substantially eliminated. Thus, the sealability of the whole bearing apparatus is improved. See, Japanese Patent No. 4286063 (also published as JP2004-354299).
In such a wheel bearing apparatus with a rotational speed detecting apparatus of the prior art, sometimes separations (peelings) or small cracks are caused in the joined portions due to the difference in the coefficient of thermal expansion between the metal core 67 and the synthetic resin cover 63. The joined portions are between the metal core cylindrical portion 67a and the cover cylindrical portion 63a as well as the joined portion between the metal core lid portion 67b and the cover lid portion 63b. Thus, it is difficult to maintain the initial sealability for a long term.